1. Field of the Invention
The present invention relates particularly to a zoom lens barrel which will be most appropriate for a camera.
2. Related Background Art
In recent years, a single zoom lens has been widely used in a single-lens reflex camera instead of a plurality of lenses having different focal lengths to avoid complicated operations required when exchanging lenses and to avoid non-handiness in carrying the lenses. For example, in a two-group type zoom lens, a zooming mechanism is provided for changing a distance between the first lens group (object side lens group) and the second lens group (camera side lens group) continuously. A photographer can obtain the required focal length within a predetermined range by operating the zooming mechanism.
There exist various types of lens barrels. In Japanese Patent Application Laid-Open No. 8-146278, a two-group type lens barrel having a rotary type zooming mechanism is disclosed. This lens barrel is composed of a fixed mount fitted to a camera in a bayonet fashion; a fixed barrel united with the fixed mount; a focus ring holding a first lens group; a straightly moving ring on which outer peripheral surface the focus ring is screw engaged; a holder for holding a second lens group; and a zoom cam barrel engaged with the straightly moving ring and the holder respectively using a cam.
The zoom cam barrel is connected with a zoom ring which is operated by hand. A photographer rotates the zoom cam barrel through the zoom ring, whereby the straightly moving ring, i.e. the focus ring, and the holder approach towards each other or move away from each other, so that the zooming is performed. Moreover, in front of the connecting portion of the zoom ring and the zoom cam barrel, a driving ring is rotatably fitted to the tip of outer peripheral portion of the fixed barrel. A key connected with the focus ring is provided extending forward from this driving ring. When the driving ring is operated by hand or automatically rotated, the focus ring moves forward or backward spirally against the straightly moving ring, so that focusing is performed.
In above-described conventional lens barrel, since the driving ring is located in front of the connecting portion of the zoom ring and the zoom cam barrel, it is difficult to shorten the total length of the barrel and consequently it became an obstacle in realizing small size and light weight. Moreover, since the driving ring is fitted to the tip portion of the fixed barrel, the outer diameter of the lens barrel as a whole is apt to be big, and carrying and handling is not easy. In addition, since the zoom ring and the zoom cam barrel are connected with each other via many parts, the fixed barrel is comparatively long and the number of mechanical parts is increased, causing the problem of an increase in manufacturing cost.